Charging device, more preferably exhaust gas turbocharger for a motor vehicle

ABSTRACT

The invention relates to a charging device, such as an exhaust gas turbocharger for a motor vehicle, with a shaft carrying a compressor wheel, with a fixing device for fixing the compressor wheel on the shaft, with at least one component fixed on the shaft together with the compressor wheel by the fixing device. It can be achieved that heat expansion of the compressor wheel through the expansion coefficient (α 3 ) of at least one component can be at least partially offset. Because of this it is possible to increase the initial clamping force with which the components are positioned or clamped on the shaft without the permissible surface pressure for the clamp components being exceeded.

The present invention relates to a charging device, more preferably anexhaust gas turbocharger for a motor vehicle with the characteristics ofthe preamble of claim 1

From DE 196 53 210 C2 a turbocharger for combustion engines is known.There, in the case of temperature fluctuations on the compressor side,thermal expansion of both the shaft and of a component such as forexample a compressor wheel arranged on the shaft, as well as heatexpansion of part regions of the surrounding housing is taken intoaccount. By at least forming a wall element arranged on the compressorhousing and facing the compressor housing of material that is softerthan the material of the compressor wheel, the compressor wheel in theevent of heat expansion upon contact with the wall element can rasp saidwall element down so far until contact between compressor wheel and wallelement just ceases to exist. Because of this, the gap between thehousing inner wall and the compressor wheel is additionally minimizedand compressor efficiency improved.

Components, too, which are arranged on the shaft on the compressor side,like the shaft proper, are subject to heat expansion in the event of atemperature increase. At present it is usual to produce at least somecomponents arranged on the shaft from the same steel type. Usually, forthe compressor wheel an aluminium or titanium material can be employedfor weight reduction. In order to prevent the formation of unbalance inthe compressor wheel the components arranged on the shaft are fixed onthe shaft through a fixing device with a corresponding initial clampingforce. In the event of a temperature increase however the compressorwheel for example of aluminium or titanium material is subject togreater expansion than the shaft on which the compressor wheel isarranged because of the higher expansion coefficient. Because of this,the clamping force with which the components are fixed on the shaft isadditionally increased by an expansion force caused through the greaterheat expansion of the compressor wheel. Accordingly, this expansionforce that occurs through the thermal expansion has to be taken intoaccount with the initial clamping force otherwise the permissiblesurface pressure of the clamped components can be exceeded and in theworst case tearing of the shaft can occur. However, it is conceivablethat the maximum permissible initial clamping force is not alwaysadequate for all application range of the components arranged on theshaft. Because of insufficient initial clamping force which in the eventof a falling temperature for example in winter can be additionallyreduced through the high expansion coefficient of the compressor wheel,slipping, twisting or tilting of the compressor wheel can occur. This inturn can result in a negative unbalance change of the compressor wheelwhich could be objected to by the customer as acoustic interference.

The present invention deals with the problem of stating an improved orat least a different embodiment for a charging device, which is morepreferably characterized by a possible increase of the initial clampingforce with which the components are fixed on the shaft, without thepermissible surface pressure of the component clamped onto the shaftbeing exceeded throughout the application range.

According to the invention, this problem is solved through the subjectof the independent claim. Advantageous embodiments are the subject ofthe dependent claims.

The invention is based on the general idea of carrying out a materialpairing of components arranged on the shaft on the compressor side andof the shaft proper so that in a predetermined temperature range anexpansion coefficient of at least one component is smaller than anexpansion coefficient of the compressor wheel. Through such a materialpairing a temperature-related expansion of the compressor wheel can bepartially offset through a lower expansion of the at least onecomponent, so that the expansion force resulting from the expansion ofthe compressor wheel and acting on the shaft is reduced. Since thecompressor wheel in combination with the at least one component inpercentage terms expands less greatly relative to the shaft than thecompressor wheel alone, the clamping force resulting from this is alsoreduced. This makes possible increasing the initial clamping force withwhich the components are positioned on the shaft through a fixingdevice, since because of the reduced expansion force that occurs duringa temperature increase the maximum surface pressure of the componentsarranged on the shaft and positioned through the fixing device is notexceeded. Because of a correspondingly increased initial clamping forceadequately stable positioning of the compressor wheel at least withrespect to its unbalance on the shaft is ensured.

In a preferred embodiment the expansion coefficient in of the at leastone component in the predetermined temperature range is not only smallerthan the expansion coefficient of the turbine wheel, but even smallerthan the expansion coefficient of the shaft. Because of this, the effectdescribed above can be increased and the initial clamping force can alsobe further increased accordingly.

Further important features and advantages of the invention are obtainedfrom the subclaims, from the drawing and from the corresponding FIGUREdescription by means of the drawing.

It is to be understood that the features mentioned above and still to beexplained in the following can not only be used in the respectivecombination stated but also in other combinations or by themselveswithout leaving the scope of the present invention.

A preferred exemplary embodiment of the invention is shown in thedrawing and is explained in more detail in the following description.

It shows, schematically, the sole FIG. 1, a compressor wheel fixed on ashaft.

As shown in FIG. 1 with a charging device 1 a compressor wheel 2 can befixed on a shaft 3 by means of a fixing device 4. In addition to thecompressor wheel 2 at least one additional component, such as a sealingbush 5, a front part region 6 of the sealing bush 5 arranged betweensealing bush 5 and compressor wheel 2 and/or a thrust washer 7 can beadditionally positioned on the shaft 3 together with the compressorwheel 2 through the fixing device 4. In order to at least partiallyoffset heat expansion of the compressor wheel 2, which because of thelow weight is produced of an aluminium and/or titanium material, in apredetermined temperature range, at least one component 5,6,7 likewisearranged on the shaft 3 and positioned through the fixing device 4together with the compressor wheel 2 is produced of a material whoseexpansion coefficient α₃ is smaller than the expansion coefficient α₁ ofthe compressor wheel 2. Because of such material pairing, a combinationof compressor wheel 2 expands with an expansion coefficient α₁ and atleast one component 5,6,7 with a smaller expansion coefficient α₃(α₁>α₃) seemed irrelative to the shaft 3 less severely than thecompressor wheel 2 by itself. As a consequence, the expansion forceresulting from the heat expansion and acting on the shaft 3 is lowerthan in the case of a compressor wheel 2 of aluminium and/or titaniummaterial and components 4,5,6,7 which are likewise arranged on the shaftand produced of the same material as the shaft 3 or have an expansioncoefficient α₂ similar to that of the shaft 3.

Usually the compressor wheel 2 and additional components 5,6,7 are fixedon the shaft through clamping by the fixing device 4. Here, an initialclamping force has to be selected so that in the event of heat expansionof all components occurring through a temperature increase by theresultant expansion force acting on the shaft the permissible surfacepressure of the clamped components 2,4,6,5,7 is not exceeded. If boththe fixing device 4 as well as the components 5,6,7 were produced of asame material as the shaft 3, only the heat expansion of the compressorwheel 2 would lead to an expansion force occurring in addition to theclamping force and acting on the shaft 3 in the event of a temperatureincrease. This happens since the expansion coefficient α₂ of the shaftbecause of the usual material pairing is smaller than the expansioncoefficient α₁ of the compressor wheel 2. In the case of a temperatureincrease the expansion of the compressor wheel 2 that occurs inter aliaalong the shaft is thus greater than the longitudinal expansion of theshaft 3. Since the axial space of the compressor wheel 2 on the shaft 3is restricted by the fixing device 4 an expansion force effect on theshaft 3 results because of the heat expansion. For this reason, theinitial clamping force with which the components 2,5,6,7 are positionedon the shaft has to be selected so that the maximum permissible surfacepressure of the components 2,4,5,6,7 clamped to each other is notexceeded even in the case of heat expansion.

It is now possible to increase this initial clamping force if at leastone of the components 5,6,7 is equipped with an expansion coefficient α₃which is at least smaller than the expansion coefficient α₁ of thecompressor wheel 2. By such a measure the expansion force that resultsbecause of the temperature increase can be reduced, as a result of whichit becomes possible to increase the initial clamping force. This in turnhas the advantage that throughout the entire predetermined temperaturerange under consideration or the operating range of the charging device1, the clamping force acting on the components 2,4,6,5,7 remains in arange in which neither the permissible surface pressure of thecomponents 2,4,5,6,7 is exceeded nor the clamping force acting on thecomponents 2,5,6,7 dropped so far that slipping, twisting or tilting ofat least the compressor wheel 2 occurs for example because of a loweringof the temperature.

Here, heat expansion follows the following formula

l ^(x)=(l ₀ +Δl)^(x) =l ₀ ^(x)(1+α·ΔT)^(x)

w:

-   -   α Length expansion coefficient    -   l Length    -   x Dimension of 1 to 3        and the forces resulting from the longitudinal expansion follow        Hooke's Law according to the formula

$F_{l} = {{\frac{E \cdot A}{l_{0}} \cdot \Delta}\; l}$

with E Modulus of elasticity

-   -   A Cross sectional area.

Consequently, because of the longitudinal expansion Δl of the compressorwheel 2 which can only develop incompletely because of the lowerexpansion coefficient α₂ of the shaft 3, expansion of the shaft 3 andcompression of the components 2,4,5,6,7 arranged on the shaft 3 occurs.

Preferably the expansion coefficient α₃ can be selected in apredetermined temperature range of the at least one component 5,6,7 sothat it is even smaller than the expansion coefficient α₂ of the shaft3. In this case, the shaft 3 would expand more greatly relative to theat least one component 5,6,7 than the at least one component 5,6,7.Because of this, a space gain occurs in the event of heat expansion upona temperature increase which is available to the heat expansion of thecompressor wheel 2. Through this material pairing the heat expansion ofthe compressor wheel 2 which accompanies a temperature increase can beoffset to a greater extent or, if suitably designed, almost entirely.This makes possible a further reduction of the expansion force thatoccurs through temperature increase. In principle, this can be carriedout with all charging devices 1 wherein for example the shaft is made ofsteel or a steel alloy and the compressor wheel is produced of aluminiumor titanium or an aluminium alloy and/or a titanium alloy. In this casethe expansion coefficient α₂ of the shaft 3 is always smaller than theexpansion coefficient α₁ of the compressor wheel 2.

Preferably, for at least one such component 5,6,7, an alloy is usedwhich because of the Invar effect of the alloy has an expansioncoefficients α₃ which is anomalously low. Such alloys, which have suchinvariance of expansion with respect to a temperature change (Invareffect) can even have negative heat expansion coefficients in certaintemperature ranges. Because of this, expansion coefficients α₃ of atleast one component 5,6,7 can be designed which are almost zero ornegative.

The principle of offsetting the heat expansion of the compressor wheel 2by at least one component 5,6,7 with a lower expansion coefficient canbe employed for any component arranged on the shaft together with thecompressor wheel 2 and positioned or clamped through the fixing device4. The components 5,6,7 can for example be designed with an expansioncoefficient α₃ that is lower compared with the expansion coefficient α₁of the compressor wheel 2. It is likewise possible to design at leastone fixing element of the fixing device 4 so that the at least onefixing element has an expansion coefficient α_(f) that is smaller thanthe expansion coefficient α₁ of the compressor wheel 2. Likewise atleast one such fixing element can be equipped with an expansioncoefficient α_(f) that is also smaller than the expansion coefficient α₂of the shaft section. As with the components 5,6,7 this can be achievedthrough an alloy having an Invar effect. Because of this, the expansioncoefficient α_(f) of the alloy of such a fixing element is anomalouslylow and the offsetting of the heat expansion of the compressor wheel 2described above can be accomplished through such a design of theexpansion coefficient α_(f). Here it is possible that such a fixingelement is designed for example as a shaft nut.

REFERENCE NUMBERS

-   Charging device-   Compressor wheel-   Shaft-   Fixing device-   Sealing bush-   Part region-   Thrust washer

1. An exhaust gas turbocharging device, comprising: a shaft carrying acompressor wheel; a fixing element for fixing the compressor wheel onthe shaft; and at least one component fixed on the shaft together withthe compressor wheel by the fixing device, wherein at least in apredetermined temperature range an expansion coefficient (α₃) of the atleast one component is smaller than an expansion coefficient (α₁) of thecompressor wheel.
 2. The exhaust gas turbocharging device according toclaim 1, wherein in the predetermined temperature range an expansioncoefficient (α₂) of the shaft is smaller than the expansion coefficient(α₁) of the compressor wheel.
 3. The exhaust gas turbocharging deviceaccording to claim 1, wherein in the predetermined temperature range theexpansion coefficient (α₃) of the at least one component is smaller thanthe expansion coefficient (α₂) of the shaft.
 4. The exhaust gasturbocharging device according to claim 1, wherein the shaft is producedof at least one of a steel and a steel alloy.
 5. The exhaust gasturbocharging device according to claim 1, wherein the compressor wheelis produced of at least one of an aluminium, a titanium, an aluminiumalloy and a titanium alloy.
 6. The exhaust gas turbocharging deviceaccording to claim 1, wherein the at least one component is designed ofan alloy, and wherein because of the Invar effect of the alloy theexpansion coefficient (α₃) of the at least one component is anomalouslylow.
 7. The exhaust gas turbocharging device according to claim 1,wherein the expansion coefficient (α₃) of the at least one component isat least one of approximately zero and negative.
 8. The exhaust gasturbocharging device according to claim 1, wherein at least one fixingelement of the fixing device has an expansion coefficient (α_(f)) whichis smaller than the expansion coefficient (α₁) of the compressor wheel.9. The exhaust gas turbocharging device according to claim 8, whereinthe at least one fixing element has an expansion coefficient (α_(f))that is smaller than the expansion coefficient (α₂) of the shaftsection.
 10. The exhaust gas turbocharging device according to claim 8wherein the at least one fixing element is designed of an alloy wherein,because of the Invar effect of the alloy the expansion coefficient(α_(f)) of the at least one fixing element is anomalously low.
 11. Theexhaust gas turbocharging device according to claim 1, wherein the atleast one fixing element is designed as a shaft nut.
 12. The exhaust gasturbocharging device according to claim 1, wherein the at least onecomponent is designed as at least one of a sealing bush, as a part ofthe sealing bush and as a thrust washer.
 13. The exhaust gasturbocharging device according to claim 2, wherein in the predeterminedtemperature range the expansion coefficient (α₃) of the at least onecomponent is smaller than the expansion coefficient (α₂) of the shaft.14. The exhaust gas turbocharging device according to claim 2, whereinthe shaft is produced of at least one of a steel and a steel alloy. 15.The exhaust gas turbocharging device according to claim 2, wherein thecompressor wheel is produced of at least one of an aluminium, atitanium, an aluminium alloy and a titanium alloy.
 16. The exhaust gasturbocharging device according to claim 2, wherein the at least onecomponent is designed of an alloy, and wherein because of the Invareffect of the alloy the expansion coefficient (α₃) of the at least onecomponent is anomalously low.
 17. The exhaust gas turbocharging deviceaccording to claim 2, wherein the expansion coefficient (α₃) of the atleast one component is at least one of approximately zero and negative.18. The exhaust gas turbocharging device according to claim 2, whereinthe at least one fixing element of the fixing device has an expansioncoefficient (α_(f)) which is smaller than the expansion coefficient (α₁)of the compressor wheel.
 19. The exhaust gas turbocharging deviceaccording to claim 2, wherein the at least one such fixing element isdesigned as a shaft nut.
 20. The exhaust gas turbocharging deviceaccording to claim 2, wherein the at least one component is designed asat least one of a sealing bush, as a part of the sealing bush and as athrust washer.